WO1997015725A1

WO1997015725A1 - Improvements in and relating to surfacing blocks

Info

Publication number: WO1997015725A1
Application number: PCT/GB1996/002599
Authority: WO
Inventors: Christopher Douglas Hodson
Original assignee: U.P.S. Limited
Priority date: 1995-10-25
Filing date: 1996-10-24
Publication date: 1997-05-01
Also published as: MX9803245A; GB9521897D0; GB2306524A; ZA968937B; JP2000503082A; AU7316896A

Abstract

A surfacing block (1) has upper and lower surfaces (2, 7) of a generally cruciform shape. Around the boundary of the surface of the block are projections (8) and/or recesses (9) for interlocking engagement with recesses and/or projections of a neighbouring block. The block has a groove (10) in its upper surface and a drainage slot in the groove (10) such that when the block is located in interlocking engagement with a neighbouring block, a drainage channel (12) extends from the upper surfaces of the blocks to the lower surfaces of the blocks. The risk of water accumulating on the upper surfaces of the blocks can therefore be reduced.

Description

IMPROVEMENTS IN AND RELATING TO SURFACING BLOCKS

The invention relates to blocks which are used principally in the paving of surfaces, for example the surfaces of roads, pavements, driveways and courtyards, especially, although not exclusively, to the paving of surfaces subjected to high forces. In particular, one aspect of the invention relates to the drainage characteristics of the paved surfaces. The invention also relates to clusters of blocks and to blocks for use in the clusters.

Paving, consisting of a plurality of surfacing blocks, should be able to withstand large forces acting upon it. Forces to be withstood include both those caused when heavy loads are placed directly on the paving and those caused by turning loads, for example a turning vehicle. Usually the paving is laid as individual blocks on a bed of sand with joints between the blocks filled with sand or other suitable filling material. On loading, the blocks are able to move small amounts relative to other blocks thereby decreasing the risk of cracking of the blocks. However, blocks laid in that way may be displaced vertically under loading or may creep horizontally under traffic due to the sandfilled joints. There are improved paving blocks having interlocking surfaces. The interlocking projections and recesses which help to provide "lock up" between blocks, allow an array of blocks to perform as a united load-bearing surface resisting both vertical and horizontal movement of the blocks. The term "lock up" is used for the purpose of this specification to describe a condition in which blocks in the paving become progressively wedged together when the paving is under traffic or subjected to loads thereby increasing the stiffness of the paving. However, in some cases in which the blocks are su ected to large loads, the "lock up" together with other factors have been found to be insufficient to avoid failure of the paving. Failure may take the form of areas of the paving sinking or of blocks creeping horizontally by an undue amount.

Another problem with known blocks which interlock is that water, for example rainwater, or other liguids can accumulate on the upper surface of the laid blocks. That may be dangerous and, for example, may cause vehicles to aguaplane on the surface of the blocks forming a paved surface. It is therefore an object of the invention to provide a block which mitigates the above problems.

According to one aspect of the invention, there is provided a surfacing block having upper and lower surfaces bounded by walls extending between the surfaces, the surfaces being of a generally cruciform shape having four arms each of which extend in a direction substantially parallel to the lower surface and substantially perpendicular to two of the other arms of the block, the block having around the boundary of its surface projections and/or recesses for interlocking engagement with recesses and/or projections of a neighbouring block wherein the block has a groove in its upper surface and a drainage slot in the groove such that when the block is located in interlocking engagement with a neighbouring block a drainage channel extends from the upper surfaces of the blocks to the lower surfaces of the blocks.

Furthermore, liquid, in particular water, on the upper surface of the block will tend to flow into the groove and along the groove to the drainage channel and through the drainage channel to the ground. Thus water is transported away from the upper surface of a block.

The cruciform blocks have been found to have improved resistance to movement when laid from that of, for example, a rectangular block having a similar distribution of projections and recesses. The arms of the cruciform block stabilise the block and if, for example, a heavy load is exerted unevenly on the block there is increased resistance to lifting compared with a known block since, if an arm of the block begins to lift from the ground, the opposite arm is forced to interlock further with adjacent blocks thus hindering further movement of the block. Resistance to movement of the block, in the form of rotation about an axis perpen¬ dicular to the surfaces, is increased when the block is interlocked with other blocks due to the projections and recesses on the arms of the cruciform interlocking with projections and recesses of adjacent blocks and hindering such motion.

Advantageously the drainage slot is in a wall of the block such that when the block is located in interlocking engagement with a neighbouring block, the drainage channel is located in the joint between the blocks.

Where the drainage slot is in a wall of the block, the drainage channel may be provided without affecting, or at least without significantly affecting, the strength and toughness of the block which could, for example, occur if the slot were provided in the middle of the block, away from the edge.

In addition to drainage slots at the joints between blocks, the block may also include slots in the middle of the block away from the edge. The number of such middle slots would be chosen such that the strength and tough¬ ness of the block was not significantly reduced, especially where the block is intended to be used for surfaces subjected to high forces.

The drainage slot may comprise, for example, an indentation, or may be equivalent to a portion of the wall, for example, part of a projection, having been removed compared with an equivalent block having no drainage slot. In that way, either the drainage slot itself or the slot of one block together with a corresponding slot of an adjacent block form the drainage channel.

While it might appear that providing a drainage channel at a joint between two adjacent blocks would significantly reduce the interlock between those blocks, it has been found that, with blocks according to the invention, any reduction of interlock is not significant to the load-bearing capabilities of a surface of the blocks having draining channels. Advantageously, the drainage channels at the joints occupy not more than 75% of the length of the joints of a block, preferably not more than 50%.

Preferably, the block includes at least six drainage slots, more preferably the block includes at least twelve drainage slots. The number of drainage slots provided will depend on, for example, the size of the blocks and their intended application.

Advantageously the direction along the length of the drainage slot is substantially perpendicular to the upper surface of the block. In that way, where the blocks are laid with their upper surfaces horizontal, the drainage slot will be vertical which may be advantageous.

Advantageously, the block has at least one pair of parallel grooves in its upper surface. The grooves help to keep water, for example, from the upper surface of the blocks and also provide a conduit for delivering the water to the drainage channels. Furthermore, where the edges of the blocks are not chamfered, the grooves tend to disguise the true shape of the blocks which is thought to be an advantage. Preferably, the block has four parallel grooves in its upper surface. Advantageously, the block has at least one pair of perpendicular grooves in its upper surface and thus a grid of grooves is formed when the blocks are laid in an array.

Clearly it is advantageous for the grooves of one block to correspond to the grooves of an adjacent block when the blocks are laid in interlocking engagement in an array so that a network of grooves is formed to transport the water to the drainage channels.

Advantageously, when the block is located in interlocking engagement with a neighbouring block, the width of the drainage channel is substantially the same as the width of the groove in which the channel is located, so that the channel is concealed but the channel is as wide as possible to provide a large opening through which the water drains from the upper surface. Advantageously, the projections and recesses extend through the entire thickness of the block. In that way the shape of the upper surface may be substantially the same as the shape of the lower surface.

Advantageously, all of the arms of the cruciform are of substantially the same length. While it is envisaged that blocks of irregular shape could be used, blocks having all of the arms of substantially the same length are more simple to lay as they need not be placed in any particular one of their possible orientations for inter- locking with neighbouring blocks. Additionally, if the lengths of the arms are the same, the load distribution across the block is more even.

Advantageously, the block has fourfold rotational symmetry about an axis substantially perpendicular to the lower surface. In that way the block is more simple to lay as explained above.

Advantageously, the length of an arm of the cruci¬ form is substantially the same as the width of the arm. The dimensions of the block indicated below may be measured by considering the plain cruciform shape from which the block is derived and measuring the relevant dimensions of the cruciform. The dimensions of blocks are usually measured as distances between joint centres, that is the distances between the centres of joints between adjacent blocks when the blocks are laid in an array.

Advantageously, the length of the block is at least 100mm. If a block which is subjected to large loads is much smaller than that length, it may be pushed into the ground. The smaller the block, the smaller is the area across which the load is distributed. Smaller blocks may be used in areas where they would not be subjected to large loads. Advantageously, the length of the block is at least 200mm, preferably about 300mm. As the size of the _bloc_k is increased, however, there is an increased risk of cracking of the block and the weight of the block increases. Therefore the length of the block is prefer¬ ably not greater than 350mm.

Advantageously, the block has at least one projec¬ tion and/or at least one recess in each side wall and en_d wall of each arm. Interlocking engagement with each adjacent block is thus achievable, thereby increasing the resistance to movement of the block.

Preferably, each side wall and end wall of each arm has one recess and one projection which extend a substan¬ tially equal distance in opposite directions from the periphery of the cruciform shape. The dimensions of the recess and of the projection are preferably substantially the same. Those dimensions relate to the notional bloc_k having its edges at the joint centres between blocks. The actual projections and recesses might not be the same where drainage slots are located at the block walls as described below.

Advantageously the thickness of the block is between about 50 and 150mm. Generally, the thicker the block the greater its cost but the greater the load that it can withstand before breaking. Above a certain thickness however, increase in thickness of the block has little effect on the toughness of the block. Preferably the thickness of the block is between about 60 and 100mm. The actual block may be provided with a chamfer around the edge of the upper surface of the block.

There may also be provided edge blocks which are formed from a section of a block as defined above and which have a straight edge along one side of the block and so may be used at the periphery of the paved surface. The spaces between the blocks in an array of b_loc_ks may be filled using sand or other suitable material. Gravel, in particular gravel having a particle size of between 2 and 5mm, is preferred because it gives better drainage than sand.

It is to be understood that where reference is made to the dimensions of the block, the shape of the block, the configuration of the block and to the cruciform shape of the block, except where from the context it is clearly otherwise, the reference is in respect of a notional block having edges at the joint centres between the actual blocks.

The size of joint between the actual blocks is usually about 3mm and the shape of the actual block will be designed to take account of the joint. Therefore, for blocks laid having a joint of 3mm between the actual adjacent blocks, the actual edge of the block would be about 1.5mm from the joint centre between actual blocks. The corners of the actual blocks may be rounded.

Paving may be laid by laying clusters of a number of blocks as one unit using a machine with clamps which places one cluster alongside others. However, in order to lay the clusters quickly and easily, effectively straight edges and lines of weakness are often created in the paving where there is little interlock between blocks. The present invention seeks to mitigate that problem.

According to another aspect of the invention, therefore, there is also provided a cluster of surfacing blocks including at least two cruciform blocks as defined above, the blocks being arranged in the cluster such that the surface of a block is substantially coplanar with the corresponding surface of an adjacent block. Clusters of blocks containing cruciform blocks interlock effectively with blocks of adjacent clusters without creating lines of weakness in the resulting paving. The cruciform block is particularly advantageous for use in such clusters as, without attachment means provided between the blocks, a cluster of blocks may be lifted by, for example, gripper arms which press against two opposite sides of the cluster and the blocks will remain held together by friction. Especially advantageous is the case in which the cruciform blocks in the cluster have dimensions such that the length of the arms equals the width of the arms, so that the orientation of the cruciform blocks in a cluster consisting of a linear array of rows of blocks is such that the direction along the length of the block is in a direction which is not substantially parallel to the direction along the length or width of the cluster. The machine holding the cluster will thus exert a turning force on the blocks, thereby increasing the extent of the interlocking engagement. Those clusters are stable and may be lifted and transported without the cluster falling apart. Clusters of cruciform blocks may be placed in position by dropping the clusters vertically downwards into a position in which the clusters interlock with adjacent clusters.

Advantageously, at least a major proportion of the blocks are cruciform blocks as defined above. If the blocks are to be used in a surface which is subjected to large loads, the maximum advantage of using the cruciform blocks may be achieved by laying the surface using mainly cruciform blocks. Clusters of cruciform blocks do not have effectively straight joints nor create lines of weakness between the clusters when a number of clusters are laid adjacent to each other. There may be provided edge blocks which have the dimensions of a section of a block and have a straight edge so that the straight section may be placed at the periphery of the paved area. It is possible that the edge blocks could be laid as part of a cluster of blocks.

The blocks may all be cruciform blocks. It would be possible to use clusters comprising two blocks, the blocks being laid by hand or using a machine but preferably the cluster contains at least four blocks. Advantageously the cluster contains rows of blocks each comprising the same number of blocks. The cluster may contain eight blocks as two rows of four blocks, or it may contain for example twelve blocks, sixteen blocks or more .

Advantageously each block in a cluster is separate from the other blocks. The blocks are thus not connected together and therefore the final surface is substantially as if each block had been laid individually.

The invention also provides a method for laying an array of surfacing blocks, the method including the step of laying a plurality of clusters as defined above over an area. There is also provided the use of a cluster as defined above in the laying of an array of surfacing blocks.

There is also provided an array of surfacing blocks, the array comprising blocks as defined above. Advantageously, the array includes a plurality of parallel grooves in the upper surface of the array. Advantageously, the distance between the grooves, measured as the smallest difference between the middle of the grooves, is not more than half of the length of a block, the length of a block being the greatest dimension of the upper surface of the block measured in a direction perpendicular to the direction along the length of the grooves. Thus advantageously at least two grooves cross each block. Preferably, the distance between the grooves is about of the length of a block. The preferred number of grooves per block will depend on the size of the blocks and the intended application of the blocks as well as aesthetic considerations.

Preferably, the array includes a second set of parallel grooves in the upper surface of the blocks and substantially perpendicular to the first. Thus the grooves give the appearance that the surface is formed of small squares and the true shape of the blocks may be concealed. Advantageously, the drainage channels are located at the joints between adjacent blocks. Thus, where the drainage channels are located in the grooves, the drainage channels are located at the intersection of the grooves and the joints. Advantageously, the grooves are provided in relation to the block so that they intersect along a length of at least one joint centre of the block (i.e. along a wall) rather than at a point (for example if the groove is perpendicular to the wall). Thus the length of the channel is increased because the length can be made equal to the length of the intersection, with the channel 'concealed' in the groove.

Advantageously, the drainage channels are located only at the joints. As described above, channels in the middle of the blocks might decrease the loading capacity of the array. However, some blocks may have some channels in the middle of the block, away from the edge. Advantageously in the array of surfacing blocks, the spacing between walls of adjacent blocks is less than 10mm other than in the region of the drainage channel. There is therefore little movement of the blocks about their laid position. Advantageously, that spacing is between 1 and 5mm, preferably about 3mm. The space between the blocks other than at the drainage channels is preferably filled with sand or other suitable filling material.

Preferably, the spacing between walls of adjacent blocks is at least 10mm at a drainage channel. More preferably the spacing between walls of adjacent blocks is about 15mm at a drainage channel. It is most advantageous, as described above, for the width of the drainage channel to be about the same as the width of a groove at the upper surface. There is also provided an array of surfacing blocks, the array comprising a plurality of clusters as described above. According to a further aspect of the invention there is provided a surfacing block having upper and lower surfaces bounded by walls extending between the surfaces, the surfaces being of a generally cruciform shape having four arms each of which extend in a direc¬ tion substantially parallel to the lower surface and substantially perpendicular to two of the other arms of - li ¬ the block, the block having around the boundary of its surface projections and/or recesses for interlocking engagement with recesses and/or projections of a neigh¬ bouring block wherein the block includes at least one drainage slot such that, when the block is located in interlocking engagement with a neighbouring block, a drainage channel extends through the thickness of the block from the upper surfaces of the blocks to the lower surfaces of the blocks. Thus water on the upper surface of the block is drained through the channels to the ground beneath the blocks.

Advantageously, the drainage slot comprises a slot in the wall of the block. As described above, it is advantageous that the channels are located at the joints between blocks so that the strength of the block is not reduced.

Advantageously, the edges of the upper surface are chamfered and, when the block is located in interlocking engagement with a neighbouring block, the chamfer forms a groove, the drainage channel being located in the groove. Thus water, for example, on the upper surface of an array of the blocks will tend to flow into the groove formed by the chamfers and to the drainage channels.

In accordance with a further aspect of the invention, there is provided a surfacing block having upper and lower surfaces bounded by walls extended between the surfaces, the surfaces being of a generally cruciform shape having four arms each of which extend in a direction substantially parallel to the lower surface and substantially perpendicular to two of the other arms of the block, the block having around the boundary of its surface projections and/or recesses for interlocking engagement with recesses and/or projections of a neighbouring block, the shape of the block being such that when a plurality of similar blocks are in an array, lock up of the blocks can occur as a result of rotation of the blocks only about an axis substantially perpendicular to their upper surface. As indicated above, for known blocks, movement of the blocks once they are arranged in an array can occur in two main ways. A block in the array may rotate about an axis substantially parallel to the upper surface of the block thereby causing part of the block to lift above the upper surface of the array and another part of the block to sink below the lower surfaces of the array. The block may also rotate about an axis substantially perpendicular to the upper surface of the block, causing turning of the block in the plane of the array and thereby increasing interlocking of the blocks. It was known that both types of movement described above contribute to lock-up of the blocks and were therefore thought to be desirable. Such movement occurred, for example, when lifting a cluster of blocks, in which clamps are applied to two sides of a cluster of blocks. As the cluster was lifted, the blocks rotated about axes parallel to and perpendicular to the upper surfaces of the blocks leading to lock up of the blocks giving an effectively rigid cluster which may be moved into position without the blocks separating and falling from the clamps. Also, where blocks have been laid on a surface, lock-up of the blocks occurs as a result of forces exerted on the blocks, for example by traffic. It has been shown in studies that the lock-up occurs as a result of rotation of the blocks about an axis parallel to their upper surface, causing tilting of the blocks and also rotation about an axis perpendicular to the upper surface of the block. Such movements are small but cause the blocks to become wedged together and to lock up.

The Applicants have now found that, surprisingly, for some shapes of blocks, lock up can occur as a result of rotation of the blocks in an array only about an axis substantially perpendicular to the upper surface of the block. Thus, unexpectedly, lock up of an array of blocks of such shapes may be obtained with substantially no lifting or sinking of the blocks in the array as described above. That is thought to be advantageous because in most cases a substantially flat upper surface is preferred. A flat paved surface is, for example, preferred where the paved area is used by vehicles and is particularly preferred where, for example, the paved area is exposed to rainfall and the water on the upper surface is to be drained, for example as described herein. The risk of puddles forming on the upper surface of the blocks may be reduced if the upper surface of the array of laid blocks is flat. As indicated above, it has been found that the shape of the blocks is important if the desired movement of the block on lock up is to be obtained.

Preferably, the length of an arm of the cruciform is substantially the same as the width of the arm. Advantageously, all of the arms of the cruciform are of substantially the same length and each side wall and each end wall of each arm has one recess and one projection which extend a substantially equal distance in opposite directions from the periphery of the cruciform shape. Advantageously, the block has fourfold rotational symmetry about an axis substantially perpendicular to the lower surface. It is thought that that is particularly important if rotation of the block on lock up about an axis parallel to the upper surface of the block is to be avoided.

Advantageously, each projection and each recess has substantially matching dimensions and comprises a pair of plane side faces which are inwardly tapered from the periphery of the cruciform shape. Most preferably, each projection and recess comprises a plane end face which is bounded by the pair of plane side faces which are outwardly flared from the end face and preferably each projection is immediately adjacent to a recess. A block having such a shape, for example having a shape as shown in Figures la and lb below, gives the desired movement of the blocks on lock up.

There may be a pattern of grooves in the upper surface of the blocks to disguise the true shape of the blocks or to aid the drainage of water from the upper surface as described above.

The blocks may also comprise drainage slots as described above. It has been found that, even where the drainage slots are located at the edge of the block, the desired movement of the block on lock up can still be obtained when the blocks are of a particular shape.

Where the blocks include drainage slots, the shape of the slots are to be disregarded when considering the overall shape of the blocks required for the desired movement of the blocks on lock up.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, of which: Figure la shows a plan view of the upper surface of a cruciform surfacing block Figure lb shows a view from the side of and below the block of Figure la Figure 2 shows a plan view from above of an array of actual blocks according to the invention, the blocks having a configuration based on the block shown in Figure 1 and including drainage slots Figure 3 shows a detail of a cross section on the line A-A of Figure 2 The shapes of the blocks shown in the Figures is shown as the shape of the joint centres between blocks when the blocks are laid in an array, unless it is stated to the contrary.

Figure la shows a surfacing block 1. The view of the block is of the upper surface 2 and shows that the block has a generally cruciform shape. The outline of the cruciform from which the shape of the block is derived is shown in Figure la by a broken line 3. The block 1 has four arms 4 which are coplanar and are perpendicular to each other. In the block shown in Figure 1, the length 1 of each arm of the cruciform is equal to the width w of each arm. Figure lb is a view from the side of the block and shows side walls 5 and end walls 6 of the arms extending between the upper surface 2 and the lower surface 7. The walls are substantially perpendicular to the upper and lower surfaces 2, 7, as can be seen from Figure lb. The upper edges of the block may be chamfered.

The block l has projections 8 and recesses 9 around the entire periphery of the surfaces 2, 7. In relation to the cruciform 3 the dimensions of a projection is the same as that of a recess. As shown in Figure la, the recess 9 is outwardly flared and has a plane inner face and plane sides and is flanked by an inwardly flared projection 8 which has a plane outer end and plane sides. The width of the projection and the recess together when measured at the broken line 3 is equal to the length of the arm and to the width of the arm of the cruciform. As shown in Figure la, the arrangement of projections and recesses is such that the arrangement is the same for each arm of the cruciform.

The projections and recesses extend through the entire thickness of the block and therefore the shape of the upper surface of the block is the same as that of the lower surface. The upper surface 2 of the block 1 includes a grid of grooves 10 comprising two perpendicular sets of parallel grooves. The distance between two neighbouring parallel grooves may be 80mm as shown in Figure 1 or may be, for example, 40mm or 160mm. It can be seen from, for example. Figure 2, that the positioning of the grooves in relation to the edges of the surface of the block to some extent hides the position of the edges of the block. Where such aesthetic considerations are important, the edges of such blocks will not be chamfered because the chamfers tend to highlight the position of the edges of the blocks. A paved surface of the blocks will therefore appear to comprise small square blocks having sides of length 80mm (for the blocks shown in Figure 2). Another important function of the grooves is to provide channels into which liquid, in particular water, on the upper surface will tend to collect as described below. Where drainage is the most important factor, and the aesthetics of the surface is less important, the pattern of grooves may be arranged differently as described below.

In one embodiment of the invention in which the blocks are used to pave an area of ground, the ground is first levelled and if necessary prepared to provide a firm base on which the blocks will lie. Usually a bed of gravel is prepared on the ground in which the blocks will be laid. The blocks are then laid over the area in an interlocking manner as indicated in Figure 2. Adjacent walls of neighbouring blocks are generally spaced apart by a distance of about 3mm (except for the areas at drainage holes as described below) to receive sand or other suitable material and the precise dimensions of the blocks should be chosen to allow for such joints. In the block shown in Figure 1, the lengths of the arms 4 of the cruciform 3 are 112.5mm and are equal to the widths of the cruciform 3 and a block will have a mean length of about three arms lengths. Those dimensions are measured relative to joint centres between blocks. The thickness of the block, that is the perpendicular distance between the upper and lower surfaces will depend on the application for which the surface is laid.

The blocks are made from concrete and are formed in moulds using standard production techniques.

As indicated above, Figures la and lb show the shape of the block as the distance between joint centres. The edge of the actual block (not shown) will therefore be generally 1.5mm within the outline of the block shown in Figure la where a standard joint size of 3mm is allowed for. The corners of the actual block may be rounded. As shown in Figure 2, the actual blocks include drainage channels 12. The drainage channels 12 extend from the upper surface to the lower surface of the blocks and are located in the grooves 11 at the joints between the blocks, in Figure 2 the actual grooves 13 are shown and have a width, measured at the upper surface 2 of the block, of about 15mm. The width of the groove chosen will depend on the number of grooves per block, the dimensions of the blocks and the application of the blocks. In the blocks shown in Figure 2, drainage channels 12 are provided at each intersection of the actual grooves and the joint centres at the edges of the blocks. The width of the drainage channels 12 is approximately the same as the width of the grooves at the upper surface 2 of the blocks and the channels are substantially vertical (i.e. perpendicular to the upper surface 2 of the blocks where the blocks are laid on a horizontal surface) and extend along the whole length of the intersection of the actual grooves 13 and the joints. Thus the drainage slots are effectively an over wide actual joint between the blocks and the grooves. For simplicity, the outline of the blocks, other than at the drainage channels, is shown as the position of the joint centres. The broken line 14 shows the position of a section of the actual edge of the block. Figure 3 shows a detail of a cross section at the line A-A of the blocks shown in Figure 2. As can be seen from Figure 3, the actual groove 13 is in the form of a truncated V-shape.

Because the drainage channels are located at the joint centres of the blocks, each block adjacent to the channel contributes equally to the drainage channel. Although the presence of the drainage channels appear to decrease the interaction between the blocks, it has been found that, for the blocks shown in Figure 2, the interlock between neighbouring blocks resists relative motion of the neighbouring blocks. Furthermore, because the drainage channels are located at the joints between the blocks, the toughness of the blocks is not significantly reduced as it might be if, for example, the channels were located near the centre of the blocks. Moreover, the location of the drainage channels at the joints, and in particular in the grooves, leads to concealment of drainage channels. In addition to the drainage channels shown in Figure 2, the blocks may have drainage channels which may be in the middle of the block. For example, the blocks may have further drainage channels at the intersection 15 of the grooves. In a further embodiment of the invention, the blocks may be laid in clusters of individual blocks. Figure 2 shows a cluster of four blocks but the cluster may comprise, for example, eight blocks arranged as a linear array of four pairs of blocks. A pair of clamps is used to lift the cluster and to move it to the area to be paved. The clamps may be bars of any suitable material. The clamp exerts a force on the cluster through contact points with the blocks; the force holds the blocks together. Due to the dimensions of the blocks in the cluster, the direction along a pair of arms 4 of the block 1 lies neither parallel nor perpendicular to the sides of the cluster and thus the pressure exerted by the clamps tends to rotate the block about an axis perpendicular to its surface. That rotation is prevented by blocks adjacent to the block and "lock up" occurs. The blocks remain securely interlocked together for as long as the force is exerted by the clamps.

The ground on which the surface is to be laid may first be prepared as described above. The cluster may be moved in the clamps to the relevant position and lowered into interlocking engagement with blocks already laid.

In an alternative design, the upper surfaces 2 of the blocks do not have grooves but the blocks include chamfers at their edges in which liquid from the upper surfaces collects and is transported to drainage channels located in the joints. In a similar way to the blocks described above in relation to Figure 2, the width of the chamfer at the upper surface of the blocks measured between the upper surfaces of neighbouring blocks is about 15mm and the joint width between neighbouring blocks is about 3mm, except at the drainage channels where an enlarged joint width of about 15mm provides a channel through which water on the upper surface of the blocks may drain.

Many other alternatives are also possible. For example, the array of blocks may be similar to that shown in Figure 2 except that they have only one set of parallel grooves 10 and therefore half the number of drainage holes as those blocks. The pattern of grooves may be any pattern in which the grooves intersect the joints of the blocks, at least some of the intersections being provided with drainage channels. In some cases the drainage channels may be located in the body of the block away from the edges, although some reduction of the toughness and therefore of the load bearing capacity of those blocks may occur. It is envisaged that in some cases no grooves or chamfers would be provided and the drainage channels would then simply be located in the upper surface of the blocks, either at a joint or away from the edges of the blocks.

Furthermore, the general shape of the block may be different from that shown in Figure la. For example, a block might have a different arrangement of projections and recesses. The shape of the periphery of the block (corresponding to the joint centres between neighbouring blocks) may be, for example, approximately a sine wave having a wavelength equal to the length of an arm 24 of the cruciform. A further alternative could have straight lines extending between the peaks, midpoints and troughs of the sine wave instead of curves, thereby forming a triangular wave. Throughout the description the drainage slots and drainage channels are described in relation to cruciform blocks and that form of the blocks is of particular advantage as is described above. However, it is envisaged that the drainage slots and drainage channels could also be applied to other blocks, for example, a generally square-shaped block corresponding to a fifth of the cruciform block, or a rectangular block corresponding to two-fifths of that block, or a block corresponding to three-fifths or four-fifths of the cruciform block. Those blocks may have around their edges a similar pattern of projections and recesses to that of the cruciform blocks described above. Those blocks may or may not have grooves on their upper surfaces and/or chamfers around their edges as described above in relation to the cruciform blocks.

Throughout the description reference is made to paving blocks. At least in the United Kingdom the terra "paving block" is usually employed for smaller paving units and the term "paving slab" employed for larger units. Usually the division is set at paving units having a length of about 300mm. In the present specific¬ ation the use of the term "paving block" is not to be taken as implying that the overall length of the unit is less than 300mm.

It has been found that lock up of an array of blocks having the overall shape shown in Figures la and lb may occur as a result of rotation of blocks only about an axis substantially perpendicular to the upper surfaces of the blocks. That has been found both for the blocks having the drainage slots as described above and also for blocks having no drainage slots at the edges of the blocks and for blocks having no drainage slots. For example, where a cluster of twelve blocks comprising four rows of three blocks is engaged by a pair of clamps, for example bars of a suitable material, on the two opposite long sides of the cluster, and the cluster is lifted by raising the clamps, there is substantially no rotation of the blocks about an axis parallel to the upper surface of the blocks. Lock up of the blocks in the cluster occurs as a result of rotation of blocks about an axis perpendicular to the upper surface of the relevant blocκ.

Claims

1. A surfacing block having upper and lower surfaces bounded by walls extending between the surfaces, the surfaces being of a generally cruciform shape having four arms each of which extend in a direction substantially parallel to the lower surface and substantially perpen¬ dicular to two of the other arms of the block, the block having around the boundary of its surface projections and/or recesses for interlocking engagement with recesses and/or projections of a neighbouring block wherein the block has a groove in its upper surface and a drainage slot in the groove such that when the block is located in interlocking engagement with a neighbouring block a drainage channel extends from the upper surfaces of the blocks to the lower surfaces of the blocks.

2. A surfacing block according to claim l, wherein the drainage slot is in a wall of the block such that when the block is located in interlocking engagement with a neighbouring block, the drainage channel is located in the joint between the blocks.

3. A surfacing block according to claim 1 or claim 2, wherein the direction along the length of the drainage slot is substantially perpendicular to the upper surface of the block.

4. A surfacing block according to any preceding claim, wherein the block has at least one pair of parallel grooves in its upper surface.

5. A surfacing block according to any preceding claim, wherein, when the block is located in interlocking engagement with a neighbouring block, the width of the drainage channel is substantially the same as the width of the groove in which the channel is located.

6. A surfacing block according to any preceding claim wherein the block has fourfold rotational symmetry about an axis substantially perpendicular to the lower surface.

7. A surfacing block according to any preceding claim, wherein the length of an arm of the cruciform is substan- tially the same as the width of the arm.

8. A surfacing block according to any preceding claim, wherein the block has at least one projection and/or at least one recess in each side wall and end wall of each arm.

9. A surfacing block according to claim 8 wherein each side wall and end wall of each arm has one recess and one projection which extend a substantially equal distance in opposite directions from the periphery of the cruciform shape.

10. A cluster of surfacing blocks including at least two cruciform blocks as defined in any of claims 1 to 9, the blocks being arranged in the cluster such that the surface of a block is substantially coplanar with the corresponding surface of an adjacent block.

11. A cluster of surfacing blocks according to claim 10 wherein all of the blocks are cruciform blocks according to any of claims 1 to 9.

12. A cluster of surfacing blocks according to claim 10 or claim 11, wherein the cluster has no effectively straight edges.

13. A method for laying an array of surfacing blocks, the method including the step of laying a plurality of clusters according to any of claims 10 to 12 over an area.

14. An array of surfacing blocks, the array comprising blocks as defined in any of claims 1 to 9.

15. An array according to claim 14, wherein the array includes a plurality of parallel grooves in the upper surface of the array.

16. An array according to claim 15, wherein the distance between the grooves, measured as the smallest distance between the middle of the grooves, is not more than half of the length of a block.

17. An array according to claim 15 or claim 16, wherein the array includes a second set of parallel grooves in the upper surface of the blocks and substantially perpendicular to the first.

18. An array according to any of claims 15 to 17, wherein the drainage channels are located only at the joints.

19. An array of surfacing blocks according to any of claims 15 to 18, wherein the spacing between walls of adjacent blocks is between 1 and 5mm where not in the region of a drainage channel.

20. An array of surfacing blocks according to any of claims 15 to 19, wherein the spacing between walls of adjacent blocks is at least 10mm at a drainage channel.

21. An array of surfacing blocks, the array comprising a plurality of clusters as defined in any of claims 10 to 12.

22. A surfacing block having upper and lower surfaces bounded by walls extending between the surfaces, the surfaces being of a generally cruciform shape having four arms each of which extend in a direction substantially parallel to the lower surface and substantially perpen¬ dicular to two of the other arms of the block, the block having around the boundary of its surface projections and/or recesses for interlocking engagement with recesses and/or projections of a neighbouring block wherein the block includes at least one drainage slot such that, when the block is located in interlocking engagement with a neighbouring block, a drainage channel extends through the thickness of the block from the upper surfaces of the blocks to the lower surfaces of the blocks.

23. A surfacing block according to claim 22, wherein the drainage slot comprises a slot in the wall of the block.

24. A surfacing block according to claim 22 or claim 23, wherein the edges of the upper surface are chamfered and, when the block is located in interlocking engagement with a neighbouring block, the chamfer forms a groove, the drainage channel being located in the groove.

25. An array of blocks, the blocks being according to any of claims 22 to 24.

26. A surfacing block substantially as herein described with reference to and as illustrated by Figures la and lb. Figure 2, and Figure 3, of the accompanying drawings.

27. A cluster of surfacing blocks substantially as herein described with reference to and as illustrated by the accompanying drawings.

28. An array of surfacing blocks substantially as herein described with reference to and as illustrated by Figure 2 of the accompanying drawings.

29. A surfacing block having upper and lower surfaces bounded by walls extending between the surfaces, the block having around the boundary of its surface projections and/or recesses for interlocking engagement with recesses and/or projections of a neighbouring block wherein the block includes at least one drainage slot such that, when the block is located in interlocking engagement with a neighbouring block, a drainage channel extends through the thickness of the block from the upper surfaces of the blocks to the lower surfaces of the blocks.

30. A surfacing block according to claim 29, wherein the drainage slot comprises a slot in the wall of the block.

31. A surfacing block having upper and lower surfaces bounded by walls extended between the surfaces, the surfaces being of a generally cruciform shape having four arms each of which extend in a direction substantially parallel to the lower surface and substantially perpen¬ dicular to two of the other arms of the block, the block having around the boundary of its surface projections and/or recesses for interlocking engagement with recesses and/or projections of a neighbouring block, the shape of the block being such that when a plurality of similar blocks are in an array, lock up of the blocks can occur as a result of rotation of the blocks only about an axis substantially perpendicular to their upper surface.

32. A surfacing block according to claim 31, wherein all of the arms of the cruciform are of substantially the same length and each side wall and each end wall of each arm has one recess and one projection which extend a substantially equal distance in opposite directions from the periphery of the cruciform shape.

33. A surfacing block according to claim 31 or claim 32, wherein the block has fourfold rotational symmetry about an axis substantially perpendicular to the lower surface.

34. A surfacing block according to any of claims 31 to 33, wherein each projection and each recess has substantially matching dimensions and comprises a pair of plane side faces which are inwardly tapered from the periphery of the cruciform shape.

35. A surfacing block according to claim 34, wherein each projection and recess comprises a plane end face which is bounded by the pair of plane side faces which are outwardly flared from the end face.

36. A surfacing block according to any of claims 31 to

35, wherein each projection is immediately adjacent to a recess.

37. A surfacing block according to any of claims 31 to

36, wherein there is a pattern of grooves in the upper surface.

38. A surfacing block according to any of claims 31 to

37, wherein the block is according to any of claims 1 to 9 or claims 22 to 24.